Some private contributions are hidden on the contributions calendar

Summary

Some private contributions are hidden on the contributions calendar (see https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/17296#note_100660048). The problem occurs for some previously created private projects. This doesn't seem to affect any newly created projects. This is not related to gitlab-ce#51161.

What is the current bug behavior?

Some private contributions in projects that were previously created are shown on the contributions list but are not included in the contributions calendar.

Relevant logs and/or screenshots

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